1. Field of the Invention
This invention relates to optical switches. Accordingly, it is the general object of this invention to provide new and improved switches of such character.
2. Description of the Prior Art
Recently optical fiber has found utility in various fields including telecommunications wherein light can be passed through an optical fiber to convey information either in digital or analog form. It is highly desirable to have light switch from one optical fiber to another and for so doing, various techniques have been suggested in the past.
Several mechanical fiber switches have been reported in the past usually involving a coil electromagnet to produce motion of a fiber, prism or a plate. Another type of switch involves a three db beam splitter followed by a modulator in each leg. These switches suffer problems of large volume, large loss, and/or difficulty in switching one fiber between more than two fibers. Various other switches are described in various United States patents.
U.S. Pat. No. 3,208,342 to Nethercot, Jr., issued Sept. 28, 1965, discloses electro-optic light coupling of optical fibers with a piezoelectric material as a coupling medium. A controllable electric field is applied across electrodes positioned opposite each other adjacent the piezoelectric material to vary the refractive index of that material. Variation of the refractive index modulates the coupling. No mechanical motion is involved.
U.S. Pat. No. 3,299,368 to Klebba, issued Jan. 17, 1967, discloses a laser light gate utilizing a piezoelectric crystal to vary the contour of one of the mirror surfaces in a laser. The variation gates the laser on and off.
U.S. Pat. No. 3,440,560 to Pole, issued Apr. 22, 1969, discloses apparatus for controlling the emission of laser light utilizing a piezoelectric crystal to move a transparent plate which frustrates the total internal reflection from a surface of laser material. This varies the critical angle for total internal reflection at this surface, and consequently varies the direction of laser light emission.
U.S. Pat. No. 3,458,829 to Pole et al, issued July 29, 1969, discloses apparatus for controlling the area of emission of laser light utilizing two piezoelectric crystals, each coupled to a respective transparent plate, each plate frustrating the total internal reflection from a respective surface of a laser material.
U.S. Pat. No. 3,650,187 to Judin, issued Mar. 21, 1972, discloses an oscillating ball which is piezolectrically driven with the ball acting as a moving lens for a beam of light.
U.S. Pat. No. 3,834,795 to Erickson et al, issued Sept. 10, 1974, discloses the use of a piezoelectric crystal to generate an acoustic shock wave. When this wave impinges on a highly reflecting Fabry-Perot resonator, the latter becomes transmitting while the shock wave passes through it. Thus, light impinging on this resonator is gated through it.
U.S. Pat. No. 3,976,358 to Thompson, issued Aug. 24, 1976, discloses the coupling of light between two parallel optical waveguides by a switchable directional coupler technique. The material between the waveguides is a semiconductor. An applied electric field creates a change in the index of refraction which modulates the optical coupling. No mechanical motion is involved.
U.S. Pat. No. 4,146,856 to Jaeschke, issued Mar. 27, 1979, discloses a reed switch in combination with associated fiber optic cables. The two optic cables, and the reed switch, are normally disengaged. Under the influence of a magnetic field, the switch closes, and the optic cables are aligned. In the absence of a magnetic field, one of the optic cables aligns with a third fixed optic cable.
British Pat. No. 1,426,475 discloses the use of the reed relay principle to switch a fiber between positions of alignment with two other fibers. In a reed relay, one of two vanes is moved between two positions, depending on whether a magnetic field is or is not applied. In the switch, one fiber is attached to the movable vane and the other two to the fixed vane. Movement of the reeds is by electromagnetic means.
In an article entitled "Piezoelectric Ceramic Transducers" by Charles Edmiston in Electronic Design, No. 18, Sept. 1, 1974, pages 78 to 82, it is stated that a piezoelectric ceramic bender takes advantage of the transverse expansion and contraction when volages are applied in a specific direction. If one of the electrode surfaces of a long thin piece of ceramic is bonded to a thin substrate so one surface is free and the other restricted, the transducer will bend when voltage is applied. The bending motion is analogous to the curve in a bimetallic strip used in thermostats. To multiply the bending action, piezoelectric transducers are placed on both sides of the substrate. Thus, when voltage is applied, one transducer expands while the other contracts.
Bimorph configurations and multimorph flexure configurations are described in an article entitled "Consider Piezoelectric Ceramics" by Dr. Thomas G. Reynolds, III, and David M. Tanka in an article published in Electronic Design, No. 19, Sept. 13, 1977, at pages 92 to 97.